This invention relates to a latching apparatus and a cover door used for removably closing an access opening in a bulk storage structure such as a grain bin.
Large bulk storage containers are commonly used to store grain for drying purposes or in anticipation of favorable market conditions. Such grain bins can be very large structures, up to ninety feet in diameter and fifty feet in height with storage capacity of up to 350,000 bushels. The grain stored in such a bin is capable of exerting substantial forces on the structure of the bin, and it is therefore very important that the structural integrity of the grain bin be maintained, since failure to do so may cause a failure of the structure.
Grain bins are typically large cylindrical structures with conical roofs. These structures are usually constructed of curved corrugated sheet metal panels which are attached to each other using bolts spaced around each edge of overlapping panels to form cylinders. These cylinders are stacked one upon another, forming a single continuous corrugated sheet metal cylinder resting on a circular base. Since much of the structural integrity of this type of structure is dependent upon continuity of the wall surface, it is important to avoid any gaps or breaks in the walls.
Most bulk storage containers of this type require an access opening in the side of the structure. Typically, this access opening permits the insertion of conveyance equipment, drying equipment, or the like, affords access to a repairman for repairs or the like. This access opening creates a structural problem for the bin such that some means must be provided to compensate for the lack of continuous supporting material in the area of the access opening. The solution to this problem in the past has been door covers over the access opening which are structurally integrated into the wall such that when the door covers are in place they act as a structural member of the grain bin. Typically these latching systems have employed tie-rods or locking cams.
When properly used, the tie-rod latching system properly secures the cover door against the access opening. However, the tie-rods are bothersome to use and for this reason they are often removed from the cover door by operating personnel. Further, since the tie-rods are a separate component of the cover door latching system, they can easily be misplaced or misused. Since tie-rods may not always be used, a minor shift or settling of the contents could bulge or spread the access opening when not properly secured by tie-rods, resulting in a critical structural failure.
The locking cam latching system employs a hand operated cam which locks into a side member of the frame around the perimeter of the access opening. This type of latch performs well at holding the cover door in place, and are also attached to the structure, thereby eliminating the possibility of removal by operating personnel. This type of latching system, however, has a disadvantage in that it is difficult and quite often uncomfortable to use. These cam latches usually have a small, thin handle positioned on the outside of the frame member of the access opening, making it difficult to use. Moreover, these cam latches require application of a substantial amount of force in order to properly lock the cover door in place. Since these cam latches are initially difficult or become very difficult to use over a period of time, they are often left unlatched, thereby failing to properly secure the door cover in a position which would provide the structural support necessary to maintain the integrity of the structure. Further, these cam latches are usually complex, multi-piece assemblies, requiring special attachment to the side of the structure.
Yet another latching system is available, which also employs tie-rods. This type of system secures the tie-rods into place through a bolting system. These tie-rods provide substantial security in integrating the door covers to the structure, but they are very difficult to use because they require special tools for removal and replacement. Since these tie-rods require special tools, and quite often these special tools are unavailable as with the cam-latching system and the other tie-rod latching system, this "tool-requiring" tie-rod latching system is often removed from, or simply omitted from the structure during assembly, thereby increasing the risk of structural failure.
A problem common to all of the above-mentioned latching systems is that the difficulties encountered in their operation, for the various reasons mentioned above, often results in failure of the operator to employ any latching apparatus at all.